This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-382448, filed Dec. 15, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a distance measuring apparatus, and more particularly to improvement in a distance measuring apparatus used for an auto focus (AF) camera and the like.
2. Description of the Related Art
There are two basic AF techniques used in cameras; and the passive type, utilizing a subject image, and the active type, utilizing a light ray incident from a camera, for measuring distance.
These techniques, however, have their corresponding drawbacks. As disclosed in, for example, Jpn. Pat. Appln. KOKAI 63-49738, therefore, various kinds of AF mode in which both modes (passive and active) are combined are proposed as a hybrid mode or a combination mode.
In the proposal in which the conventional passive AF mode and active AF mode mentioned above are combined, the following matters are not sufficiently stated. For example, there is no sufficient description on improvements in either the passive or active AF modes in weak scenes.
For example, if a subject is distanced, the contrast is low and the scene is bright, and it is difficult for passive AF to utilize an image to accurately measure a distance because of the low contrast. Further, in the active AF mode, the distance cannot be accurately measured because it is too great. That is, there is a scene which is difficult to be focused even for a hybrid AF camera.
It is, therefore, an object of the present invention to provide a distance measuring apparatus capable of stably measuring a distance irrespective of the brightness or the distance.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
A first object of the present invention is to provide a distance measuring apparatus comprising:
a sensor for detecting an incident light ray from an object;
a light source including a first light source and a second light source which is different from the first light source;
a circuit for detecting a reflected light component from the object based on an output from the sensor when the light source emits a light ray;
a circuit for selecting either the first light source or the second light source to cause light generation by comparing an output from the detection circuit and a reference value; and
a circuit for setting the reference value in accordance with an output from the sensor when the light source does not emit a light ray.
A second object of the present invention is to provide a distance measuring apparatus comprising:
a sensor for detecting an incident light ray from an object;
a light source for projecting a light ray onto the object;
a circuit for detecting a reflected light component from the object based on an output from the sensor when the light source emits a light ray;
a distance measurement circuit for calculating a distance to the object based on a quantity of reflected light from the object which is detected by the detection circuit and caused due to the projected light ray from the light source; and
a circuit for determining a correction algorithm used when the distance measurement circuit calculates the distance to the object based on an output from the sensor when the light source does not emit a light ray.
A third object of the present invention is to provide a distance measuring apparatus comprising:
a light source capable of switching a quantity of light;
a sensor for receiving a light ray from an object;
a circuit (distance calculation circuit) which calculates a distance to the subject based on an output from the sensor, and has a passive distance measurement mode for performing calculation based on a position of an incident light ray to the sensor when the light source does not emit a light ray, and an active light quantity distance measurement mode for performing calculation based on a quantity of incident light to the sensor caused due to light generation of the light source; and
a circuit for determining a quantity of light of the light source.
A fourth object of the present invention is to provide a distance measuring apparatus comprising:
a first light projection source for projecting a first distance measurement light ray onto an object;
a second light projection source for projecting a second distance measurement light ray whose intensity is higher than that of the first distance measurement light ray to the object;
a sensor array for converting an incident light distribution from the object into an electrical signal;
first distance determining means for determining a distance to the object from an output from the sensor array when the first distance measurement light ray is projected;
second distance determining means for determining the distance to the object from an output from the sensor array when the second distance measurement light ray is projected; and
selecting means for selecting either the first distance determining means or the second distance determining means based on an output level of the sensor array when the first and second distance measurement light rays are not projected.
A fifth object of the present invention is to provide a distance measuring apparatus comprising:
a sensor array for converting a distribution of light incident from an object into an electrical signal;
a light projection source for projecting a distance measurement light ray onto the object;
reflection signal light extracting means for extracting a reflection signal light ray from an output from the sensor array when the light projection source projects a light ray;
judging means for judging an output level of the sensor array when the light projection source is not actuated; and
distance measuring means for determining distance measurement based on an image signal output obtained by the sensor array when the extracting means is not actuated, or a judged level switched by an output from the judging means and a reflected light quantity signal according to a projected light quantity of the light projection source.